Prevent repeat entries in SharePoint list

[ehertel]

In a column on my SharePoint list, the entries must either be equal to a specific value, or unique from every item in the list. For example, when a user adds a value in this column, it must either be "****" or a four digit number that is unique from all other numbers in that column. A valid list would be:

0001

0002

****

0004

****

0005

I want to make sure that any values in this column are either exactly "****" or unique from any other number value, but I can not do this with the existing enforce unique values option as this would not allow for any repeats of "****". Is there a way to do this with Power Automate and have it present an error message for any number repeats?

[#2]

@ehertel Instead of using power automate, use power apps to customize list forms as it will show the error message to user before saving list item. If you use power automate, list item will be saved then flow will run. In this case you can inform user maybe using email & then you have to delete the list item.

In power apps you can check for existing values in list using formula while saving the item. If value found in list you can notify user using Notify() function else submit the list form. 

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